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TRG-TRC016-EN 61
period three
System Variations
notes
A third method of using an “alternate” fuel is actually to use the same fuel
(electricity) but to use it at a different time. The highest electricity costs occur at
the time of highest demand. For example, a real-time-pricing rate for electricity
may be $0.50/kWh at times of peak demand during the day but only $0.03/kWh
at night. By using either ice or chilled water to store cooling capacity at night
when the cost of electricity is low, and then using that stored energy to help
cool the building during the day when the cost of electricity is high, total electric
costs can be reduced substantially. Although thermal storage does not use a
different fuel, it is certainly an option for avoiding high electricity costs during
peak periods.
Low-Flow Systems
Building owners are becoming more conscious about how improved efficiency
reduces system operating costs and overall environmental impact. Typically,
the largest piece of equipment in the chilled-water system is the water chiller.
However, it is also the most efficient piece of equipment in the system.
Figure 68 shows the dramatic improvements in chiller efficiency, at standard
ARI conditions, since 1970. High-efficiency compressors and motors,
economizers on multiple-stage centrifugal compressors, more heat-transfer
tubes, and tubes with special geometry to enhance heat transfer in both the
evaporator and condenser, have all contributed to these efficiency
improvements. Manufacturers continue to strive to improve chiller efficiency
by redesigning chiller components.
Chiller Efficiency Improvements
chiller efficiency (kW/ton)
chiller efficiency (kW/ton)
1970
1970
year
year
1980
1980
2000
2000
COP
COP
kW/ton
kW/ton
1990
1990
chiller efficiency (COP)
chiller efficiency (COP)
0.9
0.9
0.8
0.8
0.7
0.7
0.6
0.6
0.5
0.5
8.0
8.0
7.0
7.0
6.0
6.0
5.0
5.0
4.0
4.0
Figure 68